arcturus; See: http://www.sw-em.com/Fuses,%20Alloca...m#Fusing_Rules

Clan; ...but Current is what does the work...no current, no work...perfect example is Derek's duff bat.

Derek; The Voltmeter you measured that Bat with, drew an extremely low and insignificant amount of current, so it measured the surface charge voltage just fine...but once the significant current required by the Starter is drawn (and we want to do some work), voltage collapses to nothing...that is why a Load Test is what should be performed on a Bat...it takes into account the internal resistance of the Bat...which should be quite low, so that when high current is drawn, only very little drops across its own low internal resistance, and almost all voltage occurs across Load...

Cheers

I would use the term potential until a circuit is made.

Ron. The AA man did the proper tests and repeated them about half an hour later. Left engine running and then switched off and tried a start. Would barely click the solenoid. He'd had a cup of tea sheltering from the pouring rain at the hairdressers where I'd taken my mum and sister. Was my sisters AA account. Alternator was working normally.

So, worked out fuse rating for headlamps. 2x60w. 120/6. x 1.25. =25.w. fuse. is that correct?

arcturus;

I'm not sure where you got the 1.25 factor (1.5 to even 2 is a good factor range for incandescents because of their inrush), and your results would be in Amps, and that would then be used as fuse rating...so short answer is: Not quite.

Looking at what the factory did as a reference: In wiring diagram of a 6V 444 (http://www.sw-em.com/444LS%206V%20Wiring%20Diagram.gif), we see 45W/40W Headlight elements (7.5A/6.6A), and a single 25A fuse upstream of the Light Switch. Nominal current calculates at 15A/13.2A (1.6/1.9 Factors)

Contrast that to the 6V 544 WD (http://www.sw-em.com/544_6Vwiring.jpg) where Headlights of similar wattage ratings are individually fused at 8A, so the factor there works out at only 1.06/1.2. (I'd be mildly concerned and on the lookout for fuse "nuisance blows" with those low factors, but I'm sure factory engineers found those values to be OK, showing judgement and actual test experience is also taken into account when specifying fuse currents!).

So long answer (taking into account standard fuse values) is...if fusing individually for 60W, I'd recommend 12 or 15A, and if fusing together, I'd use 25A or even 30A (assure wire gauge is suitable for expected normal condition current!).

Hope that helps.

i am using 2.5 gauge wire. 2x60w bulbs on one fuse for the time being. I will be altering to 1x60w with 112amp fuse, when i get another fuse block. The w/v x1.5 I plucked from the internet I am using H4 6v 60/55w P43T light bulbs

arcturus;

You should double-check the charts to see if 2.5mm2 wire has a suitable cross-sectional area for the expected current, but otherwise that sounds OK.

Cheeers